Introduction to Resource Recovery

Our way of life has caused the availability of resources to be placed under a great deal of stress. The continued exploitation of resources has led to a decrease in their availability. The overconsumption of resources has severely affected the environment which is now impacting human health. Resource recovery is an effective way of meeting shortages in the supply of resources while also encouraging sustainability. Resource recovery refers to the retrieval of resources from waste. Various resources such as metals, chemicals, fuel, and nutrients can be recovered from solid wastes. The following are some ways by which resources are recovered:

• Organic municipal wastes can be converted to renewable forms of energy through the anaerobic digestion of bacteria. Through the anaerobic digestion of organic wastes, the bacteria release methane and carbon dioxide. These gases, collectively known as ‘biogas’, can be captured and used in place of other conventional dwindling energy sources. All organic wastes and human and animal faecal wastes can be used to produce biogas.
• Old, used cooking oil can be converted to biofuel. Biofuel can be used as an alternative source of fuel in the transportation sector.
• Bioethanol can be retrieved from agricultural waste from mills and farms. Bioethanol is a fuel that can also be used as a substitute for petrol in road transport vehicles.

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Material Separation and Processing Techniques

‘Material Separation’ is the process by which the different elements of waste are separated. Separation allows wastes to be processed effectively. The common types of separation processes are:

1. Picking

Here, the components of waste are separated at the source by manual labour.

2. Screening

The screening process is important in the separation of small-sized waste particles. First, waste material is placed in an instrument called a ‘screener’. The screener contains a screen of a fine mesh. Once the material is placed inside, the screener is switched on and begins to vibrate. The vibrations cause the materials to bounce around. The small particles will fall through the meshed screen and into a bin. This process is an effective one in separating out particles by size. Smaller waste particles do not need a long processing time; hence early separation saves time and energy.

3. Magnetic Separation

Magnetic separation is extremely useful in separating ferrous materials from non-ferrous ones. Unsorted material is kept under the exposure of a powerful magnet. This is done either on a conveyor belt or in a chamber. Ferrous material will be attracted by the magnet, while the rest of the non-ferrous material will be left behind. So now the ferrous material can then be appropriately recycled. The non-ferrous material will go on to be separated in a different way and later processed.

The processing of wastes after separation improves the efficiency of solid waste management systems. Processing is also an important step in the recovery of resources from waste and in preparing materials for resource recovery. Let’s look at the processing methods for different types of waste.

1. Paper processing

Paper waste is processed at a paper recycling station. Here, paper is separated according to its types like newspapers, craft papers, etc. After separation, it is washed with soap water. The washing ensures that material like glue and ink is removed from the paper. The paper residue is then mixed in a container to make a slurry. The slurry is then left to dry as large, thin sheets from which paper is recovered again.

2. Glass processing

Glass is first sorted and separated according to its type. After this, all contaminants from the glass are removed. It is then de-coloured, dyed, and moulded according to the requirements of the desired final product.

3. Metal processing

After being separated into ferrous and non-ferrous, metal wastes are then compacted in a compacting machine. The compaction of wastes allows the recycling process to be more efficient. It is then shredded into tiny particles for easy management and handling. Finally, it is melted and purified. In its molten state, it can be moulded into sheets and ingots. These sheets and ingots are sent to manufacturers and industries for reuse, and thus the cycle continues.

Materials Recovery Facilities

A Material Recovery Facility (MRF, often pronounced ‘murf’) is a facility that receives, separates, and sorts material thrown out as waste that can be recycled. It is an important component in the process of resource recovery and in recycling programs. An MRF uses a combination of manual labour and machinery equipment to recover waste materials and prepare them to be shipped to recyclers. The main operating units in a typical MRF are:

1. Pre-sorting

At this stage, waste is sorted manually. Contaminated and bulky material is separated from those that are clean and can be recycled.

2. Mechanical sorting

After pre-sorting, the materials are sent through mechanical instruments that segregate different waste streams. Instruments based on a wide variety of physical principles such as fluid dynamics, electromagnetics, etc., are used.

3. Screening

The material is then screened so that its segregation into two or more size classes can be achieved.

4. Detection and route system

Here, the sorting of material that could not be sorted in the above methods is done. The different grades of paper, glass, etc., are segregated in this system.

5. Size reduction

Those materials that are too large for recycling or further processing are reduced in size. This allows further processing or recycling to be easily achieved.

Objectives of Waste Processing

• Protect the environment from negative impacts of the generation of waste and the over-consumption of resources.
• Protect human health from the generation of hazardous and industrial waste.
• Provide the urban poor with better living conditions and economic opportunities.
• Help in maximizing the economic benefits of waste management at no additional costs.

To achieve all the objectives mentioned above, it is important that societies understand and accept them as well. Society, the primary producer of waste, must adopt practices that support sustainable waste management systems. The practices should be implemented at work and at home. Society’s perception of waste as an undesired by-product of their activities has to change. The potential of waste as a resource must be recognized.

Biological Conversion

Composting is a biological process that involves the decomposition of organic wastes by microorganisms. The end product of decomposition is compost, a material that is rich in nutrients. Composting helps divert tons of waste away from landfills. Composting increases microbial activity improves the structure of soil and its porosity, helps sequester enormous amounts of carbon, and is an efficient way of recycling plant nutrients. There are many benefits to composting with zero environmental or public health impacts.

So what exactly can be composted? Everything biodegradable can be composted! Every organic material ranging from agricultural waste to seafood processing waste, is suitable for composting.

Though composting is an extremely easy process, utmost care must be taken to provide an ideal environment for microorganisms involved in the process. Without a thriving microbial population, the decomposition of organic wastes will be ineffective. There must be a perfect balance between moisture, oxygen, and nutrients in a composting environment.

Vermicomposting is similar to normal composting. However, here instead of microorganisms, earthworms break down organic matter. After the organic matter has been broken down, a residue called ‘casting’ or ‘worm casting’ is left behind. Castings are rich in nutrients and are extremely valuable as organic fertilizers. Vermicomposting is an effective way of turning organic wastes back into a resource since earthworms make very good composting agents. They eat almost half the amount of their weight every day. Their populations increase in a relatively short period of time. Since earthworms are taken out of their natural environment and put into a composting bin, perfect conditions must be created for their survival.

Recovery of Thermal Conversion Products

Thermal conversion (or thermal processing) is a method of resource recovery. The method uses heat to obtain other forms of energy from biomass (plant and animal-derived material). This is a renewable and sustainable form of energy. There are three main methods used in the thermal conversion of wastes. They are:

1. Incineration or combustion

Incineration or combustion is when biomass is burned in the presence of oxygen. The energy released from this burning is mainly used to produce electricity. For example, the heat energy released from furnaces or boilers is used to drive wind turbines which in turn produce electricity.

2. Pyrolysis

Pyrolysis involves exposing biomass to high temperatures under low oxygen conditions. This is done in a chamber that is under high pressure. The result is the production of liquid fuel and a solid material called ‘char .’Char has high carbon content and can be used in place of charcoal. Pyrolysis involves the partial combustion of biomass.

3. Gasification

In gasification, biomass does not undergo combustion at all. Gasification is the process of converting organic material/biomass to gases like carbon monoxide, hydrogen, and carbon dioxide. Gasification is carried out in the presence of high temperatures and a controlled amount of oxygen. The gas obtained from this process is used in the production of biofuels.